Treatment of lubricating oil fractions with a solvent for the polycyclic constituents



United StatcsPatent O TREATMENT on runitrcsrnrci on FRACTIONS WITH A SOLVENT ron'rnn PoLroYcLIc CON- STITUENTS William K. T. Gleim, ls'la'ndLalre, lit, a'ssignor, by nicsne assignments, to Universal Oil Products #Cornpany, Des Plaines, Ill, a corporation of Delaware 7 No Drawing. Application December 18, 1957 Serial No. 703,512

11 Claims. or. 208-354 I This invention relates to aprocess' for removing cyclic hydrocarbons, particularly polycyclic aromatic and naphthenic hydrocarbons from the lubricating oil fractions of petroleum to thereby enhance the lubricating qualities of the oil. More specifically, this invention concerns a process for extracting naphthenic and aromatic constituents, particularly polycyclic hydrocarbons from lubricating oils by an extraction process effected in two stages, in the first stage of which the lubricating oil feed stock is contacted with a short-chain alkyl monoether of a dihydric phenol, followed by contacting the rafiinate from recovering the rafiinate phase of the latter extraction as such extraction with a nuclearly-substituted alkyl derivative of a mono-alkyl ether of a dihydric phenol and the desired product of the process.

In accordance with one of its embodiments this invention relates to a process for enhancing the lubricating properties of a mineral lubricating oil which comprises mixing said oil with a'mono-alkyl ether of a polyhydric phenol in which the alkyl radical of the ether group contains from 1 to 4 carbon atoms at a temperature sufiicient to maintainsa id ether and said oil in a substantially liquid phase and to dissolve the major proportion of the polycyclic hydrocarbon components of said oil, thereafter separating a first extract phase comprising said ether containing dissolved polycyclic hydrocarbons from a first rafiinate comprising the non-extractedportion of said oil, thereafter mixing at liquid phase conditions said first raflinate with a nuclearly alkyl-substituted monoalkyl ether of a polyhydric phenol in which the nuclear alkyl-substituent and the alkyl radical of the ether group contain from 1 to 4 carbon atoms, and separating a second treated oil rafiinate from a resulting second extract comprising said alkyl-substituted ether.

Suitable lubricating oil feed stocks for treatment herein are selected from certain fractions of mineral oil origin having relativelyhigh boiling points, particularly of petroleum origin, which have lubricating properties, generally consisting of. a mixture of isomeric parafiin hydrocarbons in which various proportions of aromatic and naphthenic hydrocarbons may be present by virtue of their presence in the lubricating oil boiling range fraction separated from the mineral oil crude. Petroleum crudes from all sources contain high boiling hydrocarbon components. of relatively high viscosity index which make such fractions suitable for use as lubricating oils, the fraction of such mineral 'oils boiling from about 509 to about 1000 Efibeing selected as the material generally suitable for lubricating oil purposes. Mineral oils from certain particular localities are especially suitable for lubricating purposes because of their highly paraffinic composition, the paraflinicity of the oil making it par ticularly resistant to degradation at the temperatures encountered in internal combustion engines. Parafiinic mineral oils are also characterized in having particularly high viscosity indices, a property which enhances the lubricating quality of the oil by increasingthe tendency Patented Nov. 24, 1959 "ice to remain as a film on the metallic surface, even at relatively high temperatures. Petroleum lubricating oil fractions derived from other localities, particularly the socalled Mid-Continent and Michigan crudes, contain relatively large proportions of aromatic and naphthenic hydrocarbons, including polycyclic aromatics and na'pl rthenes which, due to their presence, decrease the desirable lubricating properties of the oil by reducing the viscosity index and increasing the tendency of the oil to deposit carbon at high bearing temperatures. Thus, the presence of polycyclic aromatics and polycyclic naphthenes in lubricating oil fractions, depreciate the desirable lubricat ing qualities of the paratfinic constituents comprising the lubricating oil. It therefore becomes desirable to remove from the lubricating oil fraction its fused-ring aromatic and naphthenic components normally present therein, even from lubricating fractions of Pennsylvania crudes which contain a relatively high proportion of paraflinic constituents. Regardless of the derivation of the crude, therefore, at least some improvement of the lubricating oil fraction thereof may be realized by treatment of the fraction in accordance with the present process to remove the polycyclic aromatic and naphthenic hydrocarbon constituents normally present to some extent in such fractions.

It has been found that the fused-ring polycyclic aroinatic constituents present in lubricating oil fractions, said constituents being responsible for the low viscosity index of the oil, may be removed therefrom without simultaneously removing too great a proportion of the desired parafiinic components of the oil by extractingthe raw oil with an mono-alltyl ether of a dihydric phenol, preferably containing a relatively short-chain alkyl ether group. After removal of the polycyclic aromatics of the lubrieating oil it becomes feasible to extract the polycyclic naphthenes, alsoresponsible for reducing the viscosity of the 'oil, with a solvent comprising a nuclearly mono-alkylsubstituted alkyleth'er of a dihydric phenol and recovering a raffinat'e from the latter extraction from which a major proportion of the polycyclic hydrocarbons have been removed from the lubricating oil fraction, the latter rafiinate residue possessing a substantially higher viscosity index and having substantially improved lubricating qualities. These extractants inboth the first and second stages of the process have the capacity to selectively dis solve the polycyclic hydrocarbons from the desired straight-chain paraflinic residue, the latter treated oil raffinate having a substantially improved viscosity index and enhanced lubricating qualities.

In accordance with the process of this invention the lubricating oil feed stock is extracted in at least two separate extraction steps, initially, (when the concentration of aromatic constituents in the lubricating oil is at a relatively high level) with a short-chain monoalkyl ether of a dihydric phenol having a relatively high solvency for aromatic hydrocarbons, but a relatively low solvency for cyclic paraflins. Following the initial contact of the first-stage extractant with the lubricating oil feed stock, the extract comprising predominantly solvent is separated, for example, by decantation from a raffinate residue lubricating oil, containing a relatively greater proportion of paraffinic to fused-ring polycyclic hydrocarbons than theinitial feed stock. After the removal of at least a portion of the aromatic components of the lubricating oil by separation of the'first-stage rich solvent phase from therafiinate'resi'due, the latter may be subjected to the second-stage extraction procedure comprising theprese'nt invention in which fused-ring polycyclic naphthenes are removed from the raffinate residue of the first-stage extraction by contacting said first-stage rafiinate with a nuclearly alkyl-s'ubstituted derivative of a moiio alkyl ether of a dihydric phenol, and recovering a second-stage raflinate from the rich solvent comprising said phenol, said raflinate having a much higher proportion of aliphatic paraflins to fused-ring polycyclic hydrocarbons than either the first-stage rafiinate or the initial fed stock. If desired, the second-stage raflinate may be subjected to a third, separate extraction procedure with a solvent of the type comprising the first-stage extractant, if desired, to remove an additional quantity of aromatic hydrocarbons for further improvement of the lubricating oil stock.

The first and second stage solvents utilized in the present process are similar to the extent that each is the mono-alkyl ether of a dihydric phenol, except that the second-stage solvent is a nuclearly-substituted mono-alkyl derivative of the type of compound comprising the firststage solvent. The structure of the first and second-stage solvents and a comparison therebetween may be had by reference to the following diagrammatic and empirical formulas for these phenolic derivatives lst-Stage Solvent 2nd-S tags Solvent wherein R, R and R are each independently selected from an alkyl radical containing from one to four carbon atoms, of branch or straight-chain configuration. More specifically, the compounds found to be suitable as extractants herein are members of the group consisting of the mono-alkyl ethers of catechol and resorcinol and their nuclearly alkylated derivatives, the nuclear alkyl-substituent and the alkyl radical of the ether group being selected from the alkyl groups containing from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl, either or both of said alkyl groups being the same or different. Typical representative compounds suitable as solvent extractants for use in the first'stage of the extraction procedure, that is, the mono-alkyl ethers of catechol and resorcinol, include, for example, guaiacol (Z-methoxyphenol), 2-ethoxyphenol, Z-n-propoxyphenol, Z-isopropoxyphenol, Z-n-butoxyphenol, 2-isobutoxyphenol, Z-tert-butoxyphenol and the corresponding rnono-3-methoxy, ethoxy, n-propoxy, isopropoxy and isomeric butoxyphenols. Typical mono-alkyl ethers of dihydric phenols containing a nuclear alkyl-substituent comprising the group of compounds hereinabove specified for use as the second-stage solvent extractant include such specific compounds as: 2-methoxy-3-rnethylphenol .(3-methylguaiacol) 2-methoxy-4-methylphenol, 2-

ethoxy-S-methylphenol, 2-ethoxy-4-methylphenol, 2-prophenol, 2-mcthoxy-3-ethylphenol, the 2-substituted ethoxy,

propoxy, isopropoxy, butoxy, isobutoxy and tertiarybutoxy, 3- and 4-ethylphenols, the corresponding alkoxy compounds substituted in the 3 and 4 positions by the n-butyl group, the isobutyl group and the tertiarybutyl group, the 3-alkoxy-2-alkyl and 4-aJkyl-substituted phe' nols. Of the above compounds suitable for effecting the second-stage extraction treatment of the first-stage rafiinate, the 3- and 4-alkyl-substituted guaiacols, par ticularly the 3- and 4-methyl, ethyl and propyl guaiacols, alone or in the form of mixtures thereof, such as certain wood tar distillates, are especially preferred herein because of their effectiveness in accomplishing the desired extraction of fused-ring naphthenes and aromatics from lubricating oils and their low cost in the present process.

The contact between the lubricating oil and phenolic solvent to thereby selectively extract the fused-ring polycyclic hydrocarbon components of the lubricating oil feed stock is effected at temperatures preferably below about 40 C. and at a pressure sufiicient to maintain the phenolic compound substantially in liquid phase during the course of the extraction. The solubilizing effect of the phenolic extraction on all classes of hydrocarbons present in the lubricating oil is substantially enhanced by increasing the temperature of extraction and it is accordingly preferred that the extraction temperature be maintained at a level below about 4 C., in order to maintain the oil and solvent in two separate liquid phases, the extract phase of which may be separated from the raflinate to thereby remove the polycyclic components in solution in the solvent.

One of the preferred procedures for effecting the present extraction process comprises intimately mixing the lubricating oil feed stock initially (that is, in the first: step) with an alkoxyphenol which is selectively miscible with the fused-ring aromatic hydrocarbon components present in the lubricating oil feed stock, thereby removing a relatively large proportion of such aromatic components, separating a raffinate comprising a partially treated oil residue, subjecting the rafiinate to a secondstep extraction, utilizing nuclearly monoalkyl-substituted alkoxyphenols which (in the substantial absence of aromatics) selectively remove fused-ring naphthenic hydrocarbons, and, if desired, subjecting the raflinate of the second-step extraction to a third-step treatment with an alkoxyphenol of the type employed as solvent in the firststep extraction (either the same as or difierent from the first-step extractant) to remove an additional quantum of aromatic recoverable from the second-step rafiinate when the naphthenes are removed. The foregoing procedure recognizes the difference in selectivity and solubility relationships of phenolic solvents for aromatic and naphthenic hydrocarbons when the phenolic solvent contains an alkyl group on the aromatic nucleus. Thus, it has been observed that when the alkoxyphenol contains, in addition to the alkyl ether group, a nuclear alkyl radical, the solubility of the aromatic components of the feed stock in the solvent solubilizes the parafiinic and naphthenic components as well and no selectivity of the solvent for aromatics is realized. If, however, a more selective solvent is employed in the initial extraction, only aromatic constituents are removed from the feed stock in the extract, leaving a separable paraffin-naphthene raflinate poor in aromatics. The latter rafiinate may then be contacted with an alkoxyphenol containing a hydrocarbon-solubilizing alkyl group to remove not only the remaining aromatic components in the rafiinate but the next most soluble class of hydrocarbons in the rafiinate, the naphthenes. The latter second-step rafiinate may be' thereafter extracted in a third-step extraction with an alkoxyphenol to remove any residual aromatics, if desired, to further improve the viscosity index of the lubricating oil. In each of the extraction steps, the contact between the solvent stream and lubricating oil charge stock is preferably countercurrent in order to increase the number of contact stages in each pass through the extractor.

In most instances substantially complete removal of the fused-ring hydrocarbons from the lubricating oil charge stock is effected by employing a solvent to feed ratio in each contact stage of from about 0.1 to l to about 10 to 1 weight proportions of phenolic compound to lubricating oil, the preferred ratio depending upon the molecular weight of the phenolic extractant, although ratios of extractant to charge stock within the range of from 1 to l to about 5 to 1 are particularly preferred.

The contact between the solvent and lubricating oil 'is effected at conditions whereby the phenol is intimately mixed with the lubricating oil, for example, by stirring, shaking, or by other means of agitation, whereby the'two substantially immiscible phases became intimately mixed within each other at the desired temperature and pressure conditions, followed thereafterby separating the. two phases, for example, by decanting the upper hydrocarbon layer from the resulting lower, rich solvent phase. Each of the respective phases may thereafter be separately treated to recoverthephenolic extractant and treated lubricating oil raffinate in their desired purities. Thus, depending upon the relative volatilities of the extractant and lubricating oil phases, respectively, the rich solvent phase maybe subjected to distillation to vaporize the relatively small proportion of phenolic extractant contained therein and thereby remove the same from the lubricating oil product which is, separately recovered; the recovered oil may also be countercurrently washed or extracted with water or caustic to remove the phenolic solvent therefrom, or a combination of both methods of recovery may be utilized to thereby remove the last traces of extractant from the treated oil. Similarly, the rich solvent phase comprising predominantly phenol ex,- tractant may be subjected to fractional distillation, depending upon the relative volatilities of the lubricating oil and extractant, respectively, to strip the dissolved fusedring aromatic and naphthenic hydrocarbons from the spent phenolic extractant. Alternatively, the rich solvent (that is, spent extractant) may be countercurrently contacted with a relatively volatile, liquid hydrocarbon, preferably a paraffinic hydrocarbon, such as n-pentane, to extract from the rich solvent the fused-ring aromatic and naphthenic hydrocarbons originally present in the lubrieating oil charging stock to thereby remove and recover the extract from the rich solvent. If desired, the volatile paraffin may be stripped from the residue of fused-ring hydrocarbons by distillation or otherwise to recover the light parafiin for recycle purposes.

One of the most effective and commercially feasible methods of removing the aforesaid fused-ring aromatics and naphthenes from the indicated lubricating oil cuts comprises the method referred to as countercurrent liquidliquid solvent extraction wherein the phenolic extractant or solvent is charged into the top of a countercurrent liquid-liquid phase contacting column and allowed to descend as a discontinuous phase (for example, in the form of droplets) through a rising stream (the continuous phase) of the lubricating oil charging stock in liquid phase, the solvent becoming progressively richer in dis solved fused-ring aromatic and naphthenic hydrocarbons as it descends downwardly through the column (being the phase of greatest density), while the liquid lubricating oil phase ascends upwardly through the column and becomes progressively leaner in fused-ring aromatic and naphthenic hydrocarbons, being removed from the top of the column for further treatment to remove the normally small amount of dissolved phenolic extractant therefrom (for example, by stripping) or as the final product of the process. If desired, the lube oil charge may be diluted to reduce its viscosity prior to the extraction with a less viscous liquid normally insoluble in the solvent,

such as 'a lower molecular weight n-paraffin hydrocarbon,

preferably a hydrocarbon boiling below about 200 C., such 'as n-pentane, or n-hexane. The rich solvent stream in liquid phase removed from the bottom of the extraction column maybe subjected to a stripping operation in a separate still, for example, by reducing the pressure thereon to thereby recover an overhead comprising the solvent. A particularly preferred method of operating the present process comprises extracting the lubricating oil charging stock in a countercurrent contacting column at ambient temperatures and atmospheric pressure, recovering the rich solvent from the lower portion of the extractor, count'ercurrentlyv extracting the rich solvent in a separate column with a relatively more volatile paraflinic hydrocarbon, recovering a washed, regenerated phenolic extractant which may be recycled directly to the initial contacting column and thereafter flash distilling the volatile paraflin from the extracted fused-ring aromatic and naphhenic tr t by' edu nsthe Pres 9;! the separated light parafiin wash effluent or distilling the effluent to vapor shtra a fin- Q hr- Hi tl sr9 q$1 of the product as well as the extract, and other means of effecting the contact between the various hydrocarbon and solvent streams employed in the process may obviously be utilized and are within the contemplated scope of this invention.

The treated, lubricating oilproducts of this invention are of enhanced lubricating qualities, in that the treat ment results in an increase in their viscosity. indices, a reduction in their aromaticity and when sulfurand nitro: gen compounds are present within, the. lubricating oil charging stock, the treatment also results, in the reduction in the content of these types of compounds, within the lubricating oil. The maleic anhydride value of the, oil (the diene number) for those. oils'con'taining olefinic. components is also substantially reduced, thereby. enhancing the stability of the oil at high temperatures, such as temperatures normally encountered by the oil in automotive and other internal. combustion engine crankcases. The reduced tendency of carbon deposition and the increasein the v cos ty' ndex oi the o l ma edly mprq cs its lubricating qualities.

e r o h p ific mb d m t o is-invsmi n a us a n the f l ow n e am e ic h weve a e o n e d d o ce il im th 1 o e n? vention in accordance therewith.

EXAMPLE 1 A M nen e oil ra on. whi ad been dewaxed by chilling i sv s on in met y e lryl kctones t9 crystallize out the wax parafiins and furfural extracted to remove aromatics was analyzed, the data yieldingthe following'information respecting the compositionof the treated oil:

1 Corresponding to hydrocarbons of CaaHse.

Its molecular weight by the cryoscopic method of determination was 388.; its bromine No. was 3.4; its Conradson carbon (10% bottoms) was 0.48 and'its probable content of hydrocarbon types was as follows:

. Percent Parafiins and naphthenes 78.8 Aromatics 19.9

On the basis of additional tests, its kinematic viscosity at F. was 44.69 cst., and at 210 F.: 6,132 cst.; its Universal viscosity at 100 F. was 208 seconds and at 210 F.: 46.3 seconds. Its, viscosity index was 88.7 and its N.P.A. color was approximately 2.5. The above lube oil fraction having the indicated physical and' chemical characteristics was extracted a IQOm temperature by means of a multi-stage solvent extraction procedure utilizing various alkoxy phenols and alkylsubstituted alkoxyphenols (indicated in the following Table I as solvents). For this purpose, 100 cc. of the lube oil was shaken at room temperature with eight, separate, equal aliquots of solvent, followed after each aliquot of solvent by decanting the oil phase from a lower layer comprising rich solvent. The slight amount of solvent which dissolves in the, extracted lube oil raflinate is re-v moved therefrom by first distilling the treated oil to a temperature of about 300 C., collecting the overhead distillate which comprises a major portion of the dissolved solvent and thereafter countercurrently washing the residue at room temperature with a dilute aqueous caustic solution (2 volumes ofl0% aqueous sodium hydroxide). The recovered, washed lube oil has the properties indi. cated in the following Table I.

v '7 Table I.Treatment.of Mid-Continent lube oil by solvent extraction, followed by caustic wash Volume of Extract, Viscosity Percent of Solvent Index Lube Oll Extracted 4-Methylgualacol 111. 4 62 4-Ethylgualacol..- 112. 2 64 d-Propylguaiacol 110. 2 68 4-Met-hyl-2 propoxyphenol 109. 67 a-Methyl-z-tert-butoxypheno 108. 0 76 4-Tert-buty1guaiacol 109. 0 76 -n-Octylguaiaco] 1 100 -Methylgualacol 113. 1 60 5-Tert-butyl6-methoxyphenoL 108. 0 76 Gualacol 118. 2 8 Z-propoxypheuol 116. 0 21 3-buyoxyphenol 8 110. 1 32 Wood tar fraction, B.P. 215250 C 117. 2 11 1 Oil and solvent mutually soluble.

1 Hydrocarbons to extract over 50% aromatic; substantially no naphthene. Ratlinate still contains aromatics.

Hydrocarbons in extract less than 50% aromatic, some naphthenlo and paraffinic. Y

4 Mostly a mixture of 4-rnethyl-, 4ethyland 4-propylguaiacol.

'It will be noted from the above results that when a nuclear alkyl group as well as an alkyl ether group occupy the dihydric phenol, the resulting solvent is not sufficiently selective to preferentially extract only the most soluble components of the lube oil and. to leave the more desirable parafiinic constituents in the raftinate phase. it will be further noted that the solvents containing an ether radical, but no nuclear alkyl group are more highly selective in extracting aromatics, but do not possess sufficient solvency to remove all of the aromatics from the lube oil stock.

Another sample of the Mid-Continent lube oil fraction indicated above is treated with silica gel, an adsorbcnt normally effective for removal of aromatic hydrocarbons from mixtures of the same with non-aromatic hydrocarbons. Although silica gel is somewhat effective for treatment of the lube oil fraction to remove aromatics therefrom, the latter treatment is not as efiectivc as the foregoing solvent extraction for the purpose of in creasing the viscosity index of the oil. Thus, by passing the oil (diluted with two volumes of n-hexane) through a bed of silica gel of sufficient quantity to adsorb all of the aromatics present in the initial oil, and thereafter distilling overhead the n-pentaue diluent, the oil thus treated is a product containing no aromatics; a substantial proportion of the naphthenes initially present therein, however, are not removed by silica gel adsorption. The recovered, treated product has the following properties:

Kinematic viscosity at 100 F.: 34.06 cst. Kinematic viscosity at 210 F.: 5.45 cst.

Universal viscosity at 100 F.: 159.6 sec. Universal viscosity at 210 F.: 44.1 secs.

EXAMPLE II In another run, a Mid-Continent lubricating oil which has been treated with methylethylketone to reduce its wax content has the following composition with respect to hydrocarbon types (other than the 9% by weight of wax removed in the MEK treatment):

Percent Paraflins +naphthenes 62.5 Aromatics 28.5

v The oil has a viscosity index of 84.7 and when passed through a silica gel column to remove its aromatic components, which are separately recovered, the paradinnaphthene rafiinate has a viscosity index of 109 and the aromatic absorbate recovered from the spent silica gel has a viscosity index of -103.

The above lube oil charge is mixed in two stages with equal volumes of guaiacol at 35 C. to separate an ex tract phase from a treated oil raffinate phase. The extract was distilled to recover a hydrocarbon extract which was 69.5% aromatic, having a viscosity index of 53. The first rafiinate layer contains 76.4% paraffins+naphthenes having a viscosity index of 111.2 and is 20% aromatic. The rafiinate thus formed has a viscosity index of 93.5. The above first-step raffinate was then extracted in four stages with equal volumes of a mixture of 4-methylguaiacol, 4-ethylguaiacol and 4-propylguaiacol in the form of a wood tar fraction having a boiling range of 215 to 250 C. The second-step extract recovered from the resulting rich solvent has a viscosity index of 91.9, contains 79.1% 'paraifins-i-naphthenes (having a viscosity index of 106.3 to 111.2), and 17.8% aromatics having a viscosity index of -128.3. The rafiinate from the above second-step treatment with alkylguaiacol solvent was subjected to a third-step extraction treatment with three equal aliquots of guaiacol to form an extract (combined rich solvent phases) having a viscosity index of 1638 and a third-step rafiinate having a viscosity index of 122, the latter raffinate consisting of 91.1% parafiins-l-naphthenes having a viscosity index of 129.7 and 8.9% aromatics having a viscosity index of 21.

Thus, by means of the above three-step extraction procedure. the lubricating oil starting material which contains 29% aromatics and has a viscosity index of only 84.7 may be extracted first with gua acol. then with a mixture of alkylguaiacols and finally again with guaiacol to yield a refined oil product containing only 9% aromatics and having a viscosity index of 122. If the latter product is passed over silica gel adsorbent to remove residual aromatics. the v scosity index is further increased to 130, a product having optimum lubricating oil qualities.

EXAMPLE III The fact that furfural does not provide as selective an extractant as the dihydric phenol derivatives is illustrated in the following run wherein a lubricating oil charge stock having a viscosity index of 88.7 and containing 78.8% parafiins-l-naphthene. having a viscosity index of 104.8, and containing 19.9% aromatics was subiccted in 8 contact stages utilizing equal al quots of furfural as solvent at an extraction temperature of 30 C. The resultant rafiinate product has a viscosity index of 91.9 and contains 83.4% naraffins and naphthenes having a viscosity index of 104.95 and 16.4% aromatics.

The same charge stock was contacted in 8 stages with equal aliquot portions of the aforesaid mixture of alkylguaiacols (i.e., 4-methyl-, 4-ethyl-. and 4-propylguaiacols in the form of the aforesaid wood tar fraction) at conditions identical to the above extractions with furfural to produce a raifinate product having a viscosity index of 111.4 containing 89% paraffins and naphthenes having a viscosity index of 118.06 and 7.4% aromatics. These results indicate that guaiacol and alkylguaiacols are much more effective as solvents for the aromatic constituents of lubricating oil than is furfural.

I claim as my invention:

1. A process for enhancing the lubricating properties of a mineral lubricating oil containing polycyclic aromatic and naphthenic hydrocarbons which comprises mix ng said oil with a mono-alkyl ether of a polyhydric phenol in which the alkyl radical of the other group contains from 1 to 4 carbon atoms at a temperature sufficient to maintain said other and said oil in substantially liquid phase and to dissolve a major proportion of the polycyclic aromatic hydrocarbon components of said oil, thereafter separating a first extract phase comprising said ether containing dissolved polycyclic aromatic hydrocarbon from a first naphthene-containing raflinate -cmpriS- ing the non-extracted portion of said oil, thereafter mixing at liquid phase conditions said first rafiinate with a nuclearly alkyl-substituted monoalkyl ether of a polyhydric phenol in which the nuclear alkyl-substituent and the alkyl radical of the ether group contain from 1 to 4 carbon atoms to dissolve polycyclic naphthenic hydrocarbon components out of said first raifinate, and separating a second treated oil raflrnate, from a resulting second extract comprising said alkyl-substituted ether.

2. The process of claim 1 further characterized in that said second raflinate is contacted at liquid phase conditions with a mono-alkyl ether of a polyhydric phenol in which the alkyl radical of the ether group contains from 1 to 4 carbon atoms and separating a third raifinate from a resulting third extract comprising said ether.

3. The process of claim 1 further characterized in that said first extract is contacted with a more volatile hydrocarbon substantially immiscible with said ether and separating the recovered hydrocarbon and ether phases.

4. The process of claim 3 further characterized in that said more volatile hydrocarbon boils at a temperature below about 200 C.

5. The process of claim 4 further characterized in that said more volatile hydrocarbon is a normal parafiin.

6. The process of claim 5 further characterized in that said normal parafiin is pentane.

7. The process of claim 1 further characterized in that said ether is a mono-alkyl ether of a phenol selected from the group consisting of resorcinol and catechol. I

8. The process of claim 7 further characterized in that said ether is a mono-methyl ether of said phenol.

9. The process of claim 8 further characterized in that said mono-methyl ether is guaiacol.

10. The process of claim 1 further characterized in that said nuclearly alkyl-substituted ether is a mixture of the alkyl ethers of guaiacol in which the nuclear alkyl a polyhydric phenol is a mixture of 4-alkylguaiacols separated as the fraction of wood tar boiling at from about 215 to about 250 C.

References Cited in the file of this patent UNITED STATES PA'EENTS 2,086,484 Towne July 6, 1937 2,220,016 Lyons Oct. 29, 1940 2,768,129 Knox Oct. 23, 1956 

1. PROCESS FOR ENHANCING THE LUBRICATING PROPERTIES OF A MINERAL LUBRICATING OIL CONTAINING POLYCYCLIC AROMATIC AND NAPHTHENIC HYDROCARBONS WHICH COMPRISES MIXING SAID OIL WITH A MONO-ALKYL ETHER OF A POLYHYDRIC PHENOL IN WHICH THE ALKYL RADICAL OF THE ETHER GROUP CONTAINS FROM 1 TO 4 CARBON ATOMS AT A TEMPERATURE SUFFICIENT TO MAINTAIN SAID ETHER AND SAID OIL SUBSTANTIALLY LIQUID PHASE AND TO DISSOLVE A MAJOR PROPORTION OF THE POLYCYCLIC AROMATIC HYDROCARBON COMPONENTS OF SAID OIL, THEREAFTER SEPARATING A FIRST EXTRACT PHASE COMPRISING SAID ETHER CONTAINING DISSOLVED POLYCYCLIC AROMATIC HYDROCARBON FROM A FIRST NAPHTHENE-CONTAINIG RAFFINATE COMPRISING THE NON-EXTRACTED PORTION OF SAID OIL, THEREAFTER MIXING AT LIQUID PHASE CONDITIONS SAID FIRST RAFFINATE WITH A NUCLEARLY ALKYL-SUBSTITUTED MONOALKYL ETHER OF A POLYHYDRIC PHENOL IN WHICH THE NUCLEAR ALKYL-SUBSTITUENT AND THE ALKYL RADICAL OF THE ETHER GROUP CONTAIN FROM 1 TO 4 CARBON ATOMS TO DISSOLVE POLYCYCLIC NAPHTHENIC HYDROCARBON COMPONENTS OUT OF SAID FIRST RAFFINATE, AND SEPARATING A SECOND TREATED OIL RAFFINATE, FROM A RESULTING SECOND EXTRACT COMPRISING SAID ALKYL-SUBSTITUTED ETHER. 